String Trimmer Head with Curved Trimmer Line Guide

ABSTRACT

A trimmer head assembly for a trimming machine. The trimmer head assembly includes a spool. The spool has a central tubular hub. The spool also has a central flange that radially extends from the hub. A trim line conduit is joined to the central flange. The trim line conduit has a first open end. The first open end leads to a first straight section. The first straight section leads to a curved central section. The curved central section leads to a second straight section. The second straight section leads to a second open end. The curved central section passes around the center of the spool. A housing is provided that receives the spool therein. When loading trimmer line into the trimmer head assembly, the shape of the conduit enables the trimmer line to pass around the central opening in the spool without binding.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/985,673, entitled, Bi-Directional Trimmer Head Spool With Curved Trimmer Line Guide, filed Nov. 16, 2007.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

In general, the present invention relates to string trimmers and the rotating heads of string trimmers. More particularly, the present invention relates to the mechanisms contained within string trimmer heads for winding or adding new lengths of trimmer line to the trimmer head.

2. Prior Art Description

String trimmer machines have been commercially sold for over a quarter of a century. In this period of time, there have been many variations to the design of the string trimmer machine and especially to the trimmer head.

The trimmer head is the part of the string trimmer machine that rotates. The trimmer head holds lengths of trimmer line that rotate with the trimmer head. The rotating trimmer line contacts and cuts vegetation as it spins.

There are many types of trimmer heads on the market. The most common types of trimmer heads are bump-feed trimmer heads and automatic-feed trimmer heads. Both types of trimmer heads contain an internal spool that holds a reserve of wound trimmer line. As the trimmer line wears away, it can be replaced from the internal spool. In a bump-feed trimmer head, a short length of line is released from the spool when the bottom of the trimmer head is impacted or “bumped” against a hard surface. In an automatic-feed trimmer head, a short length of line is released from the spool when a predetermined change in centrifugal forces occurs that indicates that the existing trimmer line has become too short.

Many problems exist with traditional trimmer head designs that contain internal spools. Primary among those problems are problems concerning the winding of new trimmer line onto the internal spool once the original supply of trimmer line is exhausted.

Any trimmer head that has an internal spool also has a housing that surrounds that spool. In order to resupply trimmer line to the spool, the spool must be accessed within the housing. In many early trimmer head designs, the internal spool was accessed by disassembling the trimmer head and removing the spool from the housing. This, of course, required the use of tools and a significant expenditure of labor and time.

Recognizing the problem, some trimmer heads have been designed where the trimmer line can be added without any disassembly. In such prior art designs, new trimmer line is threaded through both the housing and the internal spool. The internal spool is then rotated relative the housing to wind the trimmer line onto the spool. This process only works when the eyelet openings in the housing are precisely aligned with a channel in the spool to create a straight open conduit that enables the trimmer line to pass directly through the trimmer head.

Many trimmer heads have such straight conduits for the reloading of trimmer line. With such trimmer head designs, the trimmer line often binds as it is advanced through the conduit. The binding occurs because the trimmer line does not lay straight as it is passed into the trimmer head. The trimmer line is almost always coiled when purchased. Consequently, the trimmer line maintains a curved bias when it is removed from its packaging. Accordingly, the trimmer line has a tendency to curve as it is passed through the trimmer head. This causes the trimmer line to bind within the trimmer head or miss the housing eyelet on the far side of the trimmer head. This problem becomes compounded when the conduit through the trimmer head is not straight.

Many trimmer heads mount around a drive shaft from the trimmer machine. The drive shaft typically passes through the center of the trimmer head. As a consequence, forming a straight conduit through the center of the trimmer head is not possible. Rather, a curved conduit must be used. The use of a curved conduit in a trimmer head is exemplified in U.S. Pat. No. 7,640,668 to Iacona, and U.S. Patent App. Pub. 2008/0053052 to Cigarini.

When a curved conduit is used, the inserted trimmer line approaches the eyelet on the far side of the housing at an angle. This angle in conjunction with the natural curved bias of the trimmer line increases the tendency of the trimmer line to bind inside the trimmer head. Consequently, a user must try multiple times to correctly pass the trimmer line through the trimmer head. This takes time and labor and causes product dissatisfaction.

A need therefore exists for a trimmer head assembly with a housing and internal spool that presents a curved conduit that passes around a driveshaft, yet does not cause the inserted trimmer head line to bind. This need is met by the present invention as described and claimed below.

SUMMARY OF THE INVENTION

The present invention is a trimmer head for a trimming machine. The trimmer head assembly includes a spool. The spool has a central tubular hub. The hub is hollow and defines a central opening that extends through the hub. The spool also has a top flange that radially extends from the hub, a bottom flange that radially extends from the hub, and a central flange that radially extends from the hub.

A trim line conduit is joined to the central flange. The trim line conduit has a first open end. The first open end leads to a first straight section. The first straight section leads to a curved central section. The curved central section leads to a second straight section. The second straight section leads to a second open end. The curved central section passes around the central opening of the hub without passing into the central opening.

A housing is provided that receives the spool therein. Eyelets are formed in the housing on opposite sides. An end cap is provided that connects with the housing and retains the spool within said housing.

When loading a new segment of trimmer line into the trimmer head assembly, the shape of the conduit enables the trimmer line to pass around the central opening in the spool without binding. Furthermore, the shape of the conduit reduces binding caused by the curve bias of the trimmer line.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is made to the following description of an exemplary embodiment thereof, considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an exemplary embodiment of a trimmer head assembly;

FIG. 2 is an exploded view of the embodiment of FIG. 1;

FIG. 3 is a cross-sectional view of the exemplary embodiment of FIG. 1, viewed along section line 3-3;

FIG. 4 is a cross-sectional view of a second embodiment of the present invention trimmer head assembly;

FIG. 5 is a cross-sectional view of a third embodiment of the present invention trimmer head assembly; and

FIGS. 6 a and 6 b show a segment of trimmer line being advanced through the exemplary embodiment of FIG. 5.

DETAILED DESCRIPTION OF THE DRAWINGS

Although the present invention trimmer head can be embodied in many ways, only three exemplary embodiments are illustrated. These embodiments are selected in order to set forth three of the best modes contemplated for the invention. The illustrated embodiments, however, are merely exemplary and should not be considered a limitation when interpreting the scope of the appended claims.

Referring simultaneously to FIG. 1, FIG. 2, and FIG. 3, a first exemplary trimmer head assembly 10 is shown. The trimmer head assembly 10 attaches to the drive shaft of a string trimmer machine (not shown), which may rotate the trimmer head assembly 10 either clockwise or counterclockwise depending upon the model of the string trimming machine being used. The trimmer head assembly 10 is comprised of three major molded plastic parts. The major plastic molded parts include a primary housing 12, a spool 14 and an end cap 16 that holds the spool 14 within the primary housing 12.

The primary housing 12 defines an open interior 18. The top surface 19 of the housing 12 is closed, except for a mounting hole that permits the passage of the drive shaft into the housing 12. The bottom of the housing 12 is open, therein providing easy access to the open interior 18 of the housing 12. The periphery of the open interior 18 of the housing 12 is defined by a cylindrical wall 19 that extends downwardly from the periphery of the top surface 19.

At least two string eyelets 20 are formed through the cylindrical wall 19. The string eyelets 20 are diametrically opposed. The housing 12 may contain thickened regions about each of the string eyelets 20 to compensate for the wearing of the plastic at the string eyelets 20. Furthermore, optional wear rings 22 may be provided within the string eyelets 20. The wear rings 22 can be made from metal, ceramic, or a hard plastic that resists contact wear better than does the plastic material of the remainder of the housing 12.

The spool 14 has a central hub 24. The central hub 24 is tubular in shape and has three primary flanges 26, 28, 30 that define two trimmer line winding areas 32, 34. A trimmer line conduit 36 is coupled to the central flange 30. The conduit 36 has a first open end 38 and an opposite second open end 39. The details of the conduit 36 are later explained.

The spool 14 passes into the interior 18 of the housing 12. The end cap 16 holds the spool 14 in place. The spool 14 has a projecting knob 40 that extends through an opening 42 in the end cap 16. Accordingly, when the spool 14 is assembled within the trimmer head assembly 10, the spool 14 can be manually rotated within the housing 12 by grasping and turning the projecting knob 40.

To load a length of trimmer line 44 onto the spool 14, the spool 14 is manually rotated until the two open ends 38, 39 of the conduit 36 align with the two eyelets 20. A free end 45 of the trimmer line 44 is then advanced into the conduit 36 through one of the eyelets 20. The advancement of the trimmer line 44 is continued until the trimmer line 44 emerges out of the opposite open end 39 of the conduit 36 and passes through the opposite eyelet 20. The trimmer line 44 can then be wound onto the spool 14 by rotating the protruding knob 40.

In order for the rewinding process to work, the open ends 38, 39 of the conduit 36 must be aligned with the eyelets 20 of the housing 12. Furthermore, the curved bias of the trimmer line 44 cannot cause binding within the conduit 36. In order to reduce the likelihood of binding, the curved bias in the trimmer line 44 is compensated for by the structure of the conduit 36.

Referring now solely to FIG. 3, it can be seen that the conduit 36 generally has an omega shape. That is, the conduit 36 has two straight sections 46, 48 and a curved central section 50. The first straight section 46 extends from the first open end 38 of the conduit 36 to the curved central section 50. Likewise, the second straight section 48 extends from the second open end 39 of the conduit 36 to the curved central section 50. The combined length of the straight sections 46, 48 is at least as long as the distance D1 between the straight sections 46, 48 that is occupied by the curved central section 50.

Each straight section 46, 48 is linearly aligned with each other and lays perpendicular to the exit planes of the open ends 38, 39. The curved central section 50 begins at an upward bend 51 having a first radius of curvature R1. The upward bend 51 transitions into a downward bend 52 having a second radius of curvature R2. Lastly, the downward bend 52 transitions into a lateral bend 53 that reorients the conduit 36 back onto its original direction. The lateral bend 53 has a third radius of curvature R3. The radii of the various bends 51, 52, 53 depend upon the radius of the central opening 42 in the spool 14. It is preferred that the various radii be between 5 percent and 20 percent larger than the radius of the central opening 42. In this manner, the curved central section 50 remains relatively close to the exterior of the central opening 42.

When the trimmer line 44 enters the first straight section 46, the first straight section 46 guides the trimmer line 44 into the curved central section 50. When the trimmer line 44 exits the curved central section 46, the trimmer line enters the second straight section 48. The second straight section 48 has a long enough length to eliminate any bias curvature embedded within the plastic of the trimmer line 44. Accordingly, when the trimmer line 44 exits the second straight section 48, the trimmer line 44 has been set on a straight path and reaches the second housing eyelet 20 without any binding.

In the embodiment described, a curved central section 50 is shown. If the incoming trimmer line 44 has a downward curve bias and the curved central section 50 curves upwardly, there is potential for the trimmer line 44 to bind. To eliminate this potential problem, two curved central sections can be made, wherein one is on either side of the central opening 42. Such an embodiment is shown in FIG. 4.

Since the alternate embodiment shown in FIG. 4 has many of the same features as the originally described embodiment, the same reference numbers will be used to describe the same features. Referring to FIG. 4, it can be seen that two curved sections 50, 60 can be created between the two straight sections 46, 48. When a segment of trimmer line 44 is inserted onto one of the straight sections 46, 48 and that segment reaches the two central curved sections 50, 60, the natural curved bias of the trimmer line 44 will cause the trimmer line 44 to enter either the first central curved section 50 or the second central curved section 60. Since the natural curved bias of the trimmer line 44 creates the selection, the trimmer line 44 is not guided against its bias and the potential for binding is removed.

In the embodiments previously described, the conduits are completely enclosed between their open ends 38, 39. This need not be the case. Parts of the conduit can be fabricated in an open fashion. Such fabrication may also result in simplified and less expensive molding tools.

Referring to FIG. 5, a third alternate embodiment of the present invention is shown. In this embodiment, a spool 70 is provided having a flange 72. A relief 74 is formed in the flange 72 of the spool 70 around the central opening 76. The relief 74 has a general rhombus shape with rounded corners. The central opening 76 is disposed in the center of the relief 74. Two deflectors 78, 79 are set within the relief 74. Both deflectors 78, 79 has an offset salient point 80. The offset salient point and the angles of the deflectors 78, 79 act to deflect the trimmer line 44 to the right of the salient point 80 as the trimmer line 44 approaches the salient point 80.

The relief 74, being generally shaped as a rhombus, has a long axis 82 between corners 83, 84 and a short axis 85 between corners 86, 87. Straight sections 88, 90 of the conduit lead into the relief 74 in the same line as the long axis 82. The straight sections 88, 89 of the conduit extend to open ends 92, 93 at the edge of the flange 72. These open ends 92, 93 are aligned with the eyelets 20 in the surrounding housing 12 of the trimmer head assembly when new trimmer line 44 is loaded into the trimmer head assembly.

Referring to FIGS. 6 a and 6 b, it can be seen that when a length of trimmer line 44 is inserted through the eyelet 20 of the housing 12 and through a straight section 88 of conduit, the free end 45 of the trimmer line 44 enters the relief 74. The trimmer line 44 advances until the trimmer line 44 contacts the salient point 80 of the deflector 78. The deflector 78 deflects the trimmer line 44 to the right of the deflector 78. The trimmer line 44 then contacts the peripheral wall 94 of the relief 74 and follows the path of that wall 94. The wall 94 of the relief 74 guides the trimmer line 44 into the opposite straight section 90.

It will be understood that two deflectors 78, 79 are provided, so it does not matter in which direction the trimmer line 44 is inserted into the trimmer head. A left-to-right insertion and right-to-left insertion operate in the same manner.

As with the earlier embodiments, the combined length of the straight sections 88, 90 of the conduit are preferably longer that the distance D2 between the straight sections 88, 90 of conduit. In the shown embodiment, this distance corresponds to the long axis 82 of the relief 74.

It will be understood that the embodiments of the present invention that are illustrated and described are merely exemplary and that a person skilled in the art can make many variations to those embodiments. For instance, radius of curvatures used in the curved section of the conduit path can be varied to accommodate different spool diameters with different sized central openings. All such embodiments are intended to be included within the scope of the present invention as defined by the claims. 

1. A trimmer head assembly for a trimming machine, said trimmer head assembly comprising: a spool having a hub, a top flange that radially extends from said hub, a bottom flange that radially extends from said hub, and a central flange that radially extends from said hub, wherein said hub is hollow and defines a central opening that extends through said hub; a trim line conduit joined to said central flange, said trim line conduit having a first open end, that leads to a first straight section, that leads to a curved central section, that leads to a second straight section, that leads to a second open end, wherein said curved central section passes around said central opening without passing into said central opening; a housing that receives said spool therein, wherein eyelets are formed in said housing on opposite sides; an end cap that connects with said housing and retains said spool within said housing.
 2. The assembly according to claim 1, wherein said first straight section and said second straight section are linearly aligned on opposite sides of said curved central section.
 3. The assembly according to claim 2, wherein said first straight section of said conduit and said second straight section of said conduit are positioned a predetermined distance apart, wherein said first straight section and said second straight section have a combined length that is at least as long as said predetermined distance.
 4. The assembly according to claim 1, wherein said curved central section contains curves having a certain radii of curvature, and wherein said central opening has a circular cross-sectional profile with a predetermined radius of curvature, wherein each of said radii of curvature is greater than said predetermined radius of curvature.
 5. The assembly according to claim 2, wherein said first straight section and said second straight section are enclosed conduits.
 6. The assembly according to claim 5, wherein said curved central section includes an open relief formed around said central opening, wherein said relief has a curved peripheral wall, and wherein at least one deflector is disposed proximate said central opening within said relief, wherein said deflector and said curved peripheral wall create a curved channel that extends from said first straight section to said second straight sectiont.
 7. A spool for a trimmer head assembly, comprising: a hollow hub that defines a central opening that extends through said hub; a flange radially extending from said hub; a trim line conduit joined to said flange, said trim line conduit having a first open end, that leads to a first straight section, that leads to a curved central section, that leads to a second straight section, that leads to a second open end, wherein said curved central section passes around said central opening without passing into said central opening, wherein said first straight section and said second straight section are linearly aligned on opposite sides of said curved central section, and wherein said first straight section of said conduit and said second straight section of said conduit are positioned a predetermined distance apart, wherein said first straight section and said second straight section have a combined length than is at least as long said predetermined distance.
 8. The assembly according to claim 7, wherein said curved central section contains curves having a certain radii of curvature, and wherein said central opening has a circular cross-sectional profile with a predetermined radius of curvature, wherein each of said radii of curvature is greater that said predetermined radius of curvature.
 9. The assembly according to claim 7, wherein said first straight section and said second straight section are enclosed conduits.
 10. The assembly according to claim 9, wherein said curved central section includes an open relief formed around said central opening, wherein said relief has a curved peripheral wall, and wherein at least one deflector is disposed proximate said central opening within said relief, wherein said deflector and said curved peripheral wall create a curved channel that extends from said first straight section to said second straight section.
 11. A trimmer head assembly for a trimming machine, said trimmer head assembly comprising: a spool having a hub and a flange radially extending therefrom, wherein said hub is hollow and defines a central opening that extends through said hub; a trim line conduit joined to said flange, said trim line conduit having a first open end, that leads to a first straight section, that leads to a central relief, that leads to a second straight section, that leads to a second open end, wherein said central relief has a curved peripheral wall; at least one deflector disposed in said relief, wherein said at least one deflector and said curved peripheral wall define a guide channel that leads from said first straight section to said second straight section around said central opening.
 12. The assembly according to claim 11, wherein said first straight section and said second straight section are linearly aligned on opposite sides of said central relief.
 13. The assembly according to claim 12, wherein said first straight section of said conduit and said second straight section of said conduit are positioned a predetermined distance apart, wherein said first straight section and said second straight section have a combined length that is at least as long as said predetermined distance.
 14. The assembly according to claim 11, wherein said first straight section and said second straight section are enclosed conduits.
 15. The assembly according to claim 11, further including a knob that is coupled to said spool, wherein said knob extends through said end cap, therein enabling said spool to be manually rotated.
 16. The assembly according to claim 11, wherein said flange is the center flange of three parallel flanges that radially extend from said hub. 